text: Another approach which is typically used in FEM is the following.
  The aim of the correction step is to ensure conservation of mass. In continuous form for compressible substances mass, conservation of mass is expressed by
  where  is the square of the "speed of sound". For low Mach numbers and incompressible media  is assumed to be infinite, which is the reason for the above continuity equation to reduce to
  The way of obtaining a velocity field satisfying the above, is to compute a pressure which when substituted into the momentum equation leads to the desired correction of a preliminary computed intermediate velocity.
  Applying the divergence operator to the compressible momentum equation yields
   then provides the governing equation for pressure computation.
  The idea of pressure-correction also exists in the case of variable density and high Mach numbers, although in this case there is a real physical meaning behind the coupling of dynamic pressure and velocity as arising from the continuity equation
   is with compressibility, still an additional variable that can be eliminated with algebraic operations, but its variability is not a pure artifice as in the compressible case, and the methods for its computation differ significantly from those with